Watch Art Cashin: Why stocks are under pressure today

CNBC's Mary Thompson and Art Cashin, of UBS, discuss the rise in crude oil, and the tremendous run in the markets in 2013.

Art Cashin says stocks are "having a little bit of difficulty" today due to weakness in the tech sector.

Cashin, UBS' director of floor operations at the NYSE, told CNBC's Mary Thompson around midday that he thinks tech stocks are being hurt by "All the concern that's being expressed in the press about the run-up in Twitter and a variety of other things."

Shares of Twitter had soared about 40 percent over two weeks but were down more than 7 percent to $67.,93 just after 1pm ET.

Looking forward, Cashin says going into next year the "assumption is you're going to get some new 401(k) money, you're going to get some new pension money... This year, 2013, the beginning was the strongest part of the year. So you might get a big kick-off day."

But after that, Cashin thinks the market could be "vulnerable" for a pullback between the middle of January and the middle of February.